Is there a way to select 'back' vertex/edges/faces without having to turn on x-ray?
I may misinterpret what you say but:


The shortcut to switch from Solid to Wireframe mode (and thus to grab a hidden vertex) is Z in 2.79 and shiftZ in 2.8.
When you are in Solid mode you can activate/deactivate the Limit Selection to Visible (2.79) or Show Whole Scene Transparent option (2.8) on the horizontal menu bar.
In 2.8, in both Edit or Object mode, use altZ to switch to transparent/not transparent.